Sampling is widely used in modem electronics for converting a continuous-time signal into a discrete-time signal. Analog-to-digital converters use sampling to convert a continuous range of analog signal levels into digital codes. Such conversions are necessary to interface real-world systems, which typically monitor continuously varying analog signals, with digital systems that process, store, interpret, and manipulate digital sampled values. Signal mixers for radio frequency and radar receivers may also use sampling. In addition, sampling may be used in signal processing for many applications, such as removing noise.
Many applications require precise sampling. For example, analog-to-digital converters must sample the input signal precisely to provide the quantizer a stable signal to digitize. Imprecise sampling is typically caused by both nonlinearities in the signal path or variations in the sampling timing. Optical sampling techniques have been proposed for applications that require high-speed, precise sampling. Optical sampling is advantageous because it can be linearized and because it can have highly precise sampling time stability.
Recently, the use of electro-optic modulators for optical sampling has been proposed. The performance of such prior art optical sampling techniques is, however, limited by intensity nonlinearities inherent in the electro-optic modulators, fluctuations in optical pulse power, and phase bias variation in the modulators.